1. Field of the Invention
The present invention relates to multi-purpose damping materials capable of absorbing vibration from various structures and, more particularly, to expandable vibration damping materials especially useful in constrained layer assemblies. In addition to the vibration damping characteristics offered by the materials of the present invention, the materials also provide excellent adhesion to various substrates, improved corrosion resistances to metal components and long term durability.
2. Description of Related Art
One relatively recent focus in the automobile industry has been to control and, preferably, the elimination of noise occurring as the result of the vibration of automobile body panels. To this end, important reductions in automobile noise levels have been achieved by the vibration damping of automobile body panels such as floor panels, door panels, roof panels, and wheel house panels, among others. To effectuate this so-called vibration damping, compositions containing fillers dispersed in binders have been widely used to coat metallic surfaces of automobile body panels to provide the desired vibration damping and/or sound deadening. For example, sheet materials of heat softenable compositions including asphalt, fillers and natural and/or synthetic elastomers have been used for sound deadening as described in detail in U.S. Pat. No. 4,133,932 which issued to Sumner.
Sheet materials as described above are presently used in the automotive industry by disposing the sheet material in contact with the desired automobile panel section and thereafter transporting the automobile body through heating ovens such as those utilized for drying paint finishes. In response to the temperatures of the oven, the sheet material softens and conforms to the contour of the automobile panel section. The softening of the sheet material must be controlled or restrained, however, so that flowing or running of the thermoplastic material does not exceed a predetermined rate at elevated temperatures. This is often problematic in that many of the vibration damping materials currently known utilize too much low molecular weight polymer(s), which results in flow problems.
Additionally, the automotive industry has been focusing on vibration damping materials which offer weight reduction over previously known compositions in order to improve fuel efficiency. To this end, polymer based expandable or foamed sound deadening sheet materials of reduced density have been considered, but are generally relatively expensive, and, thus, are considered to be cost prohibitive. The increased expense in foamed sheet materials results from the high concentration of polymers required to provide acceptable functional integrity. In an attempt to reduce material costs, a class of vibration damping materials has been developed which employ asphaltic materials, which in turn reduces the amount of polymers required in the composition. These materials also tend to suffer from unacceptably high flow rates.
For a further understanding of the general nature of vibration damping materials and various constructions under which such materials are employed, reference can be made to U.S. Pat. Nos. 4,456,705 which issued Jun. 26, 1984, to McCarthy; U.S. Pat. No. 4,734,323 which issued Mar. 29, 1988, to Sato et al.; U.S. Pat. No. 5,213,879 which issued May 25, 1993 to Niwa et al; and U.S. Pat. No. 5,300,355 which issued Apr. 5, 1994, to Minufe et al., among others.
Although numerous vibration damping materials and constructions are known and currently employed in the automotive industry, heretofore, the known vibration damping materials have failed to provide or have provided only on a limited scale one or more functions including ease in application, expandability to provide a complete fill between substrates, adhesion to substrates formed from a variety of different materials without requiring pretreatment of the substrate surface with adhesives and/or primers, long term storage capability without requiring separation sheets between contiguous layers, enhanced structural integrity for the components to which the material is applied and enhanced corrosion resistance, among others. It is therefore the object of the present invention to provide a vibration damping material composition which performs each of these functions. Still further, the vibration damping material compositions of the present invention serve to shift structure borne noise which is not fully damped to different frequencies that are more easily treated with conventional interior acoustic treatments such as sound absorbing foams and fibrous mats, among others.